It's a terrific film, and claims to be based on facts. It shows how one US Congressman may have influenced the course of history.
Congressman Charlie Wilson happened to spot on TV that the Afghan mujahideen were getting smashed by the Soviet Union because the Soviets had far better weapons. The mujahideen were fighting using a few WW II rifles while the Soviets had tanks and aircraft. So Wilson decides to lobby for more money and weapons for the mujahideen.
The rest is known. The mujahideen get their Stingers and their AKs and RPGs and eventually bleed the Soviet Union pretty much to death.
When the Soviets leave, the Congressman has a huge party. He asks CIA's station chief in Afghanistan why he doesn't look overjoyed. The guy narrates a Zen story. It goes something like this: